With the rapid progress of the information-oriented society in recent years, optical information recording media, which enable by far higher density recording than magnetic recording media, are popularly utilized and actively studied. As the optical information recording media, known are a read-only type, in which information has been recorded beforehand and with which users can only read information; a write-once type, with which users can record and read information; and a re-writable type, with which users can record/read/erase information. Of these recording media, the write-once type media are being widely used as media which store bulk data compactly, because they are generally low-cost and excel in storage stability.
Of the write-once optical information recording media, a single-plate type of CD-R (CD-recordable), which is made up of a recording layer of organic dyes, a reflecting layer of metal provided on the recording layer and a protective layer provided on the reflective layer, and a plate-bonding type of DVD-R (DVD-recordable) are commonly and widely used.
The CD-R or DVD-R records information in the form of signals which are generated with changes in the organic dyes in its recording layer caused by irradiating the recording layer with laser beams from its substrate side. Moreover, various types of writers using a high-output semiconductor laser, as recording devices, and of software for information recording are commercially available. In recent years, a great number of CD-R recording devices which record at high speeds, 32 to 52× to the conventional recording speed, have been sold. And DVD-R recording devices which record at speeds of 4× or more have also been on the market. In high-speed recording, recording is performed in a shorter time than ordinary writing, but on the other hand, it requires high power laser irradiation; consequently, the margin required for the record reading characteristics narrows down. And problems have been indicated particularly of deterioration of jitter characteristics, which has not been tangible at ordinary recording speed, and increase in loading on a laser.
To overcome these problems, attempts have been made to form sharp and better-shaped pits in a shorter time even in high speed recording, from the viewpoints of the pyrolitic behavior and exothermic behavior of dyes in the recording layer, by causing pyrolitic behavior of dyes in the recording layer at a time by laser irradiation and increasing the speed of weight loss in pyrolysis or by making the peak of exothermic reaction sharp, as disclosed in Japanese Patent Laid-Open Nos. 09-058123, 10-188341 and 11-025504. However, the contents disclosed in the above documents are to improve the pyrolitic behavior of dye by using a special metal azo dye or cyanine dye or adding a quencher to a dye, and they do not provide sufficient improving effects.
In the meantime, attempts have been made to introduce a metallocene derivative and/or a ferrocene derivative into a dye composition in the recording layer by adding and/or binding the same to the dye composition, as disclosed in, for example, Japanese Patent Laid-Open Nos. 7-098887, 8-118800 and 11-70732, WO 97/23354 and WO 00/09522.
It is mentioned in Japanese Patent Laid-Open Nos. 7-098887, 8-118800 and 11-70732 that organometallic compounds such as metallocene derivatives and/or ferrocene derivatives are highly effective in improving the pyrolitic characteristics of dyes and the recording characteristics of the recording layer. Further, Japanese Patent Laid-Open No. 11-70732 discloses in column 0012 that the effect of adding the above described organometallic compounds, such as metallocene derivatives and/or ferrocene derivatives, is clearly different from that of adding the chelate compounds of transition metals used as singlet-oxygen quenchers, which are added for stabilizing the recording layer and improving the light-fastness of the same.
WO 97/23354 and WO 00/09522 disclose that the trouble of dye recovery/recycle can be improved by chemically linking a metallocene derivative and/or a ferrocene derivative to the side chain of the dye in the recording layer or to the axial substituent of the central metal.
The inventors of the present invention have also confirmed that to make high-speed recording characteristics better, the best measure is to allow organometallic compounds, such as metallocene derivatives and/or ferrocene derivatives, to act on the dye in the recording layer to improve the pyrolitic behavior of the dye.
However, it is impossible to fully accomplish higher sensitivity and better jitter characteristics, which are required for high-speed recording these days, by mixing and adding, or just linking organometallic compounds, such as metallocene derivatives and/or ferrocene derivatives, to the dye in the recording layer, and such recording media are not always sufficiently compatible with read-only CD.
In the meantime, the linking process of metallocene compounds requires many steps, which gives rise to a problem of increasing manufacturing cost.